Straightening apparatus



Aug. 26, 1947. A. v. DE FOREST 2,426,390

STRAIGHTENING APPARATUS Filed Nov. 17; 1944 2 Sheets-Swat 1 Aug. 26,1947.

A. V. DE FOREST STRAIGHTENING ArfAuws Filed Nov.. 17, 1944 AIM)! 2Shanta-Sheet 2 INVENTOR Patented Aug. 26, 1947 STRAIGHTENING APPARATUSAlfred V. de' Forest, Marlboro, N. 11., assignor to The BaldwinLocomotive Works, a corporation of Pennsylvania Application November 17,1944, Serial No. 563,931

2 Claims. (Cl. 153-32) This invention relates generally to materialstesting and processing, and more particularly to apparatus for measuringor utilizing what is known as deviation from proportionality in therelationship between load and strain, load and deflection, or stress andstrain, torque and twist, etc.

The factors of stress and strain are usually autographically recorded ormanually plotted in the form of the well-known stress-strain diagram andautographic recorder equipment for such purpose has been highlydeveloped and in wide use. However, another relationship between stressand strain, namely, deviation from proportionality, has long been knownand used but the diagram for the same has been effectively produced onlyby a very laborious method of manual plotting. Nevertheless, there aremany practical problems involving the use, shop handling, and testing ofmetallic and non-metallic materials where the deviation fromproportionality in the relationship between the above functions of loadand strain, etc., provides information of great value both technicallyand commercially. For instance, in materials testing a certainpercentage of deviation from proportionality is frequently specified asrepresenting the yield strength particularly with certain types ofnon-ferrous metals or with heat treated alloy steels having noreasonably definite yield point. On the other hand, in straightening orbending a pipe, engine crankshaft, heat treated rod or other material,the

operation is usually performed by guessing or by a mere visual anduncontrolled procedure as will be explained later although in someinstances the amount to which a member must be deformed to straighten orbend it has been mathematically determined by deviations fromproportionality. All of these operations and uses as heretofore based onsuch proportionality curve involved tedious manual or mental operationsthat by their complexity are slow and therefore undesirable except incompelling situations.

It is one objector my invention to provide improved apparatus forutilizing or measuring the critical features of the above-mentionedrelationships rather than the relationships themselves.

Another object is to provide an improved apparatus for utilizing ormeasuring the deviation from linearity in a simple, direct and positivemanner with a high degree of accuracy, sensitivity and responsiveness.

In accomplishing the foregoing, I have broadly provided electricalsensitive means responsive to the individual components of therelationship in question and also means for directly obtaining thedivergence of that relationship from linearity. In the preferredembodiment of my invention I make use of bonded wire strain gages as thesensitive elements, although I can equally well use any other well-knownelements which are electrically responsive to load, strain, deflection,etc., such as electromagnetic gages of various types, capacity typegages, carbon pile gages, carbon strip gages; in fact, any device whoseelectrical impedance varies with the quantity involved.

Other objects'and advantages will be more apparent to those skilled inthe art from the following description of the accompanying drawings inwhich:

Fig. 1 is a load-displacement curve;

Fig. 2 is a diagrammatic illustration of my invention applied to a pipeor rod straightening operation;

Fig. 3 is a wiring diagram of a responsive circuit that may be employedwith my pipe straightening operation;

Fig. 4 is a curvature gage that may be employed for determining thestraightness of a shaft or the like in accordance with the principles ofmy invention;

Fig. 5a illustrates a conventional plot of stress against strain;

Fig. 5b illustrates how the above stress-strain curve can be recast toshow only the deviations from a modulus line specifically showingdeviations of strain;

Fig. 6 is a weigh bar and extensometer adapted to be employed in myimproved combination of elements;

Fig. 6a is an integral weigh bar and specimen; and

Fig. 7 is a diagrammatic arrangement of mechanisms for producing astress-strain diagram of the type shown in Fig. 5b.

In order to appreciate the significance of my improved apparatus, I haveshown in Fig. 1, by may of simple illustration, a load displacementcurve which is characteristic of a great many materials, notably metals.Fig. 1 may, for example, represent the load displacement curve whichwould be obtained in a straightening or bending press under operatingconditions and Fig. 2 shows schematically the mechanism and factorsinvolved in the straightening operation. The piece or specimen to bestraightened or bent is supported on the bed of a press through a-pairof usual transverse supports or rests I. A piston or ram 2 exerts aforce or load to bend the specisecured to a fixed base and the other endhavin a point contact with the specimen at any desired part thereof. Forconvenience, I have shown strain-sensitive bonded wire Sages l and Penmembers 2 and 3 respectively for the purpose of measuring the load anddeflection, although as above stated any other electrically responsivedevices would serve the same purpose.

Considering Fig. 1 to represent the relation between load anddisplacement, or deflection, of the arrangement shown in Fig. 2, it isknown that if the loading starts at 5 and is progressively increased, asubstantially linear relationship holds up to a more or less indefinitepoint 6, beyond which the relation deviates from linearity along somesuch path as 6 to 'I. It now the load is removed at I and reduced tozero it is characteristic of many materials that the deflection willreturn to a point 8, such that the permanent set between points 5 and 8is very nearly equal to the curvature offset C. Where this is not quitetrue, it is a simple matter to determine experimentally the relationbetween the two quantities.

The load displacement characteristic of Fig, 1 can thus be used toadvantage in such operations as straightening, since it is quitepractical to measure offset C as the loading, or straightening process,proceeds, without having to removethe load. Supp se, for example, thatthe out-of-true of member I has been determined by rotating the memberand observing the output of deflection pickup 3; the out-of-true isfound by taking onehalf of the total reading so obtained. Now if load isapplied until offset C in Fig. 1 is equal to the out-of-true of memberI, it will be found that the member will be straight and true when theload is removed. In some instances it may be necessary to repeat theprocess to obtain perfect straightness but with a little practice on thmaterial and member involved the work can be done very expeditiously bymy method.

In present practice the straightening is done by a process oftrial-and-error in which there is little or no direct control of theamount of straightening being done. My invention makes direct controlpossible and does so by simple and easy-tooperate means.

In a further embodimentof my invention I provide means for measuring orutilizing directly the curvature offset C which avoids the necessity forhaving a plot such as Fig. 1. To accomplish this,

I oppose gage 4 against gage I in a bridge circuit so that the bridgeremains balanced over the elastic or linear range, as from 5 to B inFig. 1. Under this condition, the unbalance of the bridge will then readthe offset C directly without the necessity of plotting load againstdeflection. As an example of such a bridge I have shown Fig. 3, it b ingunderstood that many other circuits may be employed for the purposewithout departing from the spirit of my invention. 7

In Fig. 3, responsive elements 4 and 4' comprise adjacent arms, beingshunted variably by contact 13 acting on resistance 9. Resistance II isdivided by contact II to form the other two bridge arms, while i0 is awell known voltmeter serving as an unbalance indicator and I2 is asource of D. C. or A. 0. power. Contact l3 may be set so that theeffects of 4 and 4' exactly canc l each other within the linear range ofmember I; this is easily seen from the fact that the shunt resistancearound 4 goes up while that around 4' goes down. Contact It serves tobalance the bridge as a whole without changing the proportionalitysetting of contact i3. In operation, the contacts l3 and H are set sothat the bridge is balanced and remains balanced as the load is variedwithin the linear range. To perform, the straightening operation theload is then increased until the unbalance indicator II) shows that thedesired permanent set has been achieved.

Instead of simply indicating the permanent set, the unbalanced voltagemay automatically control the operation of the press so as to releasethe applied load. For instance, an adjustable electrical contact l0 canbe positioned anywhere around the circumference corresponding to thedegree of unbalance and deflection required for a given correction bythe applied load. Closure of this contact by the hand of instrument l0will reverse a usual and well-known reversible pump, or of a main valve,of a hydraulic press, thereby to relieve the load.

One particular advantage of my invention, not hitherto attained by othermeans, will be seen from the following considerations. It is known thatif an originally bent shaft is straightened by cold bending in a singleoperation, an unbalanced internal stress is produced leaving compressionon the original concave side, and tension on the convex side. Suchresidual stresses will tend to cause the shaft to again become bentunder the action of small repeated loads. To correct this situation theproper procedure is to overbend the part by an amount slightly less thanthe original out-of-straightness, and to reduce the overbend bysuccessive steps, gaging. first from one side and then from the other.The more steps the less will be the residual unbalanced stress. Byapplying the measurement method above described a few reverse bendingsof graduated amounts would produce substantially the same result, andgreatly improve the stability of shape of such articles as shafts,including engine crankshafts, oil well drill pipe, guns and riflebarrels, etc.

If a 'more accurate measurement of the straightness of member i in Fig;2 is necessary, so that the deflection of the press bed and the supportblocks is not involved, the deflection gage may be of the form indicatedin Fig. 4. This represents an instrument as disclosed in my copendingapplication Serial No. 523,159, filed February 19, 1944, for measuringthe average radius of curvature between H and J by means of the fourwire gages l5 and I5 applied to a flexible beam to which is attachedthree knife edges or contacts as shown at H, J and K. By resting such aninstrument on an accurate surface plate, the condition of balance of thegages may be determined. venient clamps or external support at H, K andJ contact the knife edges which are obviously of a character as not toindent the surface on which they lie.

Two such radius of curvature gages may be used simultaneously at degreesto each other in which case any side bending of the shaft duringstraightening may be noted and corrected by further operation. In casethe shaft is to be bent to a desired radius instead of to a straight,gages of the same character may be provided. This case occurs in variousknife bending machines.

It will be apparent to anyone skilled in the art that there are manyother practical applications Slight spring pressure from any conthat canbe advantageously made of the principles of my invention. In fact, myinvention applies to any case where it isdesirable to utilize the offsetfrom linearity in the relationship between two quantities, both of whichcan be made to change the impedance of corresponding electrical devices,the offset being obtained by opposing the'outputs of the responsivedevices so that substantially the output of the combination arises onlyas a result of the offset.

As another example of the application of my invention, I have providedan improved stressstrain recording or indicating device in which theconventional plot of stress against strain, as typified by Fig. 5a isreplaced by the well-known plot or indication showing only thedeviations from the modulus line l6, this having heretofore been made bytedious calculations and manual plotting. The resulting plot isillustrated in Fig. 5b, where the strain is thedeviation referred toshown on an enlarged scale. tage of such a plot as that shown in Fig. 5blies in the great ease with which the proportional limit H can bedetermined, as compared with that in Fig. 5a. In existing stress-strainprocedure the accuracy of the plot of Fig. 5a has to be exceedingly highor the scale very large in order to afford the desired accuracy. With mymethod the accuracy of plot, Fig. 51), need not be excessive and thedesired information is available at a glance. In fact,for manyapplications, a

I simple indicating meter will suflice for observing the essential data.

To illustrate one means for accomplishing the desired result, I haveshown in Figs. 6 and 7 a convenient means for varying the strain of aspecimen or member |8. A weigh bar member I9 is provided to measure loadand as is customary this member is made sufliciently large so that itoperates at all times within its elastic range while the specimen I8 isunder test even to the point of destruction. Member I!) may be made ofany desired elastic material and may be adapted to carry the load onmember l8, as shown in Fig. 6, or it may be of the same material as andintegral with l8, as shown in Fig. 6a. For convenience, I have shownstrain gages of the form disclosed in Ruge Patent No. 2,316,975,although any other convenient electrically sensitive gages may beemployed equally well. Bonded wire strain gages a, b, c, d, e, f, g, hare the sensitive elements. These gages, as shown in Fig. 7, areconnected in circuits and control certain mechanisms for producing astress-strain diagram of the type shown in Fig. 5b. The sensitiveelements (a-d) of Fig. 6 are connected into a strain bridge and theother elements (e-h) into a stress bridge. A suitably guided platen 2|is driven in the direction of the stress axis by a motor 22 and screw22', the motor being actuated through an amplifier 23 by the unbalanceof a. circuit 26. A suitably guided pen arm 24 is driven vertically inthe direction of the strain axis by motor 25 and a screw 25', the motorbeing actuated through an amplifier 28 by the unbalance of a circuit 21.The rotatable screw-s 22' and 25' are threaded in nuts fixed in the penarm and platen. A pair of potentiometers 29 and 30, actuated by motionof platen and pen arm respectively through contact arms 29 and '30formed on members 2| and 24, provide voltages opposing the unbalancevoltage set up by the stress and strain bridges. When either circuit 26or 21 is unbalanced, the corresponding amplifier actuates its motor soas to reston the condition A particular advan-- of balance; in doing so,the pen or stylus plots 8- stress-strain diagram of the type shown inFig. 5b as the loading progresses.

1 While the\ output of the stress bridge controls the platen motiondirectly, it is to be observed that the pen arm 24 is controlled by asignal resulting from the opposition of selected fractions of theunbalanced voltages of the stress and strain bridges. A pair ofadjustable contacts 3| and 32 permit arbitrary selectionof the relativemagnitudes of the opposing voltages. Thus it is easily seen that I canadjust the contacts 3| and 32 so that pen arm 24 does not move while member l8 of Fig. 6a is stressed within its linear range, and that this armwill only move as a result of departure from linearity in the relationbetween stress and strain. Bridge balancing adjustments 33 and 34provide balance adjustment of the bridges independent of theproportionality adjustments 3| and 32. In place of the stressstrainrecorder shown I may employ a simple deviation indicator, as suggestedbefore, when a plot is not required; in this event, circuit 26 iseliminated and circuit 21 terminates in a galvanometer or other suitableindicator instead of in potentiometer 3|).

The opposed'bridge circuit 26 per se is an invention of Arthur C, Rugeemployed by him in a spring tester apparatus. The circuit is employedhere for purposes of illustration as one means to carry out a detail ofmy invention. It will be clear that I could equally well use the circuitof Fig. 3 by making gage element 4 responsive to stress and gage element4' responsive to strain. While many other equivalent circuits might beemployed, yet the present disclosure serves to illustrate means forobtaining independent adjustment of zero balance and of the ratio of thetwo'essential measurements involved.

As Ruge has shown in his spring tester disclosure, the spring stiffnessor modulus of elasticity of specimen |8 can be read oif directly fromthe settings of contacts 3| and 32 once the linearity balance conditionis set up. Thus, the slope of the modulus line N5 of Fig. So can be readfrom a calibrated dial by leaving one adjustment, say 3|, fixed, andproviding a calibrated scale for adjustment 32 expressed in terms ofmodulus of elasticity.

From the disclosure herein it is seen that the variou embodiments of myinvention whether they relate to shaft straightening or recording can bebroadly identified as apparatus for automatically indicating ordetermining deviations from proportionality between displacement of thematerial and the force incident to such displacement. This force may beconsidered broadly herein as including stress, torque and loading forcewhile the displacement will be broadly considered as strain per se anddeflection. Strain is an actual incremental displacement within thematerial itself produced by load applied to the material in the same waythat deflection is a displacement of the material induced by a loadapplied thereto. My improved apparatus pro-- vides an automatic meansfor indicating the occurrence, as well-as the extent, of deviation fromproportionality in a simple, direct and effective manner and which canbe operated with ease, dispatch and precision without the need of anymental calculation or manual plotting.

It will of course be understood that various changes in details ofconstruction and arrangement of part may be made by those skilled in:maaaao the art without departing from the spirit of the invention asset forth in the appended claims;

I claim:

1. Apparatus for straightening a bent member comprising, in combination,means for supporting the bent member at two points which allow themember to be turned approximately 180 and which support the memberduring deflection thereof to straighten the same. strain meanselectrically responsive to displacement of the member when turnedthereby to determine the extent of misalignment of the member andconsequently the extent to which it is necessary to bend thestraightening load the member will assume a position of substantialalignment.

2. The combination set forth in claim 1 further characterized in thatthe displacement responsive means comprises a bending beam having oneend fixed and the other end bearing against the underside of the memberand the load straightening means is positioned to engage the member onthe upper side thereof opposite to said bending beam.

VAL-FRED v. or: FOREST.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,346,981 Manjoine et a1. Apr.18, 1944 2,356,763 Keinath Aug. 29, 1944 2,252,464 Kearns, Jr., et al.Aug. 12, 1941 2,316,975 Ruge Apr. 20, 1943 2,381,173 Browne, Jr. Oct.24, 1944

